#389 Crash after deleting category referenced by the Wizard

[Christa Runge]

The following issue was seen at svn 3288.

Scenario:
- Create a database with wizard (Language) and select this database
- Press the Edit Button and delete the category related to the new language
- Press the button for the Data Wizard
Expected behaviour:
The wizard re-creates the missing categories gracefully and proceeds with creating cards
Observed behaviour:
The application crashes.

[Mathias Kussinger]

Fixed in svn3504. We now check the categories when starting the database wizzard.